The present invention relates to a ceramic capacitor and ceramic compositions therefor; and, more particularly, to reduction resistive dielectric ceramic compositions suitable for use as a dielectric layer of a ceramic capacitor having internal electrodes made of a base metal such as Ni and a ceramic capacitor fabricated by employing such ceramic compositions as a dielectric layer thereof.
Recently, a base metal, e.g., Ni, is widely used in forming internal electrodes of multilayer ceramic capacitors for the purpose of reducing manufacturing costs. In case the internal electrodes are composed of the base metal, it is required that chip-shaped laminated bodies including therein the internal electrodes be sintered in a reductive atmosphere in order to prevent an oxidization of the internal electrodes. Accordingly, a variety of reduction resistive dielectric ceramic compositions have been developed.
Recent trend towards ever more miniaturized and dense electric circuits intensifies a demand for a further scaled down multilayer ceramic capacitor with higher capacitance. Keeping up with such demand, there has been made an effort to fabricate thinner dielectric layers and to stack a greater number of the thus produced dielectric layers.
However, when the dielectric layers are thinned out, a voltage applied to a unit thickness intrinsically increases. Accordingly, the operating life of the dielectric layers is shortened and thus a reliability of the multilayer ceramic capacitor is also deteriorated.
It is, therefore, an object of the present invention to provide highly reliable dielectric ceramic compositions and ceramic capacitors prepared by employing such dielectric ceramic compositions in forming dielectric layers thereof, wherein the dielectric ceramic compositions exhibit such electrical characteristics as a dielectric contstant equal to or greater than 3000, capacitance variation of xe2x88x9215% to +15% (based on a capacitance obtained at a temperature of +25xc2x0 C.) in the temperature range from xe2x88x9255xc2x0 C. to +125xc2x0 C., a dielectric loss xe2x80x9ctanxcex4xe2x80x9d of 3.5% or less and an accelerated life of 200,000 seconds or greater.
In accordance with the present invention, there is provided a dielectric ceramic composition comprising: 100 mole parts of oxides of Ba and Ti, a ratio Ba/Ti being 0.970 to 1.030; 0.25 to 1.5 mole parts of an oxide of Re, Re representing one or more element selected from the group consisting of Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Y; 0.2 to 1.5 mole parts of an oxide of Mg; and 0.03 to 0.6 mole parts of oxides of one or more elements selected from the group consisting of Mn, V and Cr.